Four benzodiazepines flunitrazepam, nitrazepam, clonazepam, and alprazolam, have been analyzed from biological matrices by dual column gas chromatography using a nitrogen-phosphorus detector (NPD) and a micro-electron capture detector (m-ECD). The recoveries of the four benzodiazepines spiked into human whole blood and plasma were 88.8 - 97.9 and 90.7 - 97.5%, respectively. The regression equations for the four benzodiazepines showed excellent linearity. The detection limits (LODs) were 0.14 - 0.95 ng/mL for whole blood and 0.13 - 0.93 ng/mL for plasma. The method is simple and sensitive for the determination of benzodiazepines in human whole blood and plasma, and may be useful in forensic science practice.